Mobile cellular networking has become increasingly commercially important because it offers enhanced performance and flexibility for many kinds of information transfer, including multimedia traffic. A mobile cellular network provides such services for a geographical area, which is divided into cells that each encompass particular geographical sections of the service area. A base station is deployed in and associated with each cell. The base stations of various cells are connected by a wireline network and are controlled by a control station using the wireline network. The control station provides the necessary computing and communication processing required to manage the network of base stations deployed throughout the service area.
Each base station services all the mobile stations within the cell surrounding the base station with desirable radio frequency (RF) signal strength. As used herein, "mobile station" is defined to include portable cellular telephones, automobile telephones, laptop and palmtop computers, personal digital assistant (PDA) equipment with wireless modems, TDMA and CDMA transceivers, pagers, and other, perhaps larger, voice and data communicating devices. The base station in each cell has a certain fixed number of radio communication channels which it can assign to calls in progress within that cell. A mobile station ordinarily communicates with the base station in the cell in which it is located over one of these radio communication channels.
The individual cells tile the entire geographical service area, but the tiling is not exact and neighboring cells overlap to form handoff regions. According to conventional practice, when a mobile station crosses the boundary of the current cell and moves into another cell while transmitting information, a communication path must be established with a new base station located in the new cell. If radio communication channels are not available in the new cell and the mobile station is not able to acquire a new channel in the new cell and relinquish its channel in its old cell before it has crossed over the boundary and moved completely into the new cell, a handoff failure has occurred and the call in progress is aborted. The probability of handoff failure, that is, the probability that a mobile call in progress will be forcibly aborted during a handoff because it could not be allocated a radio communication channel in the new cell, is a major criterion for evaluating the quality of a cellular network system. Accordingly, minimizing the probability of handoff failure is desirable in any cellular network system.
In order to minimize the probability of handoff failures, an effective mobile cellular network ought to continuously decide how best to allocate the limited set of available radio communication channels in a cell to new calls originating within the cell and handoffs that migrate into the cell from neighboring cells. This task is impeded by the inability of the base station located in a cell to handle all the new calls originating within the cell as well as the handoffs that migrate into the cell from neighboring cells. The state of mobile cellular networking could be advanced and the probability of handoff failures and transmission errors could be substantially minimized if there were a better way to handle overloading of a base station with excessive communication with mobile stations and if better warnings that a mobile station will soon enter a new cell were issued to the base station located in and associated with the new cell.